Up to the seventies, the evolution of massive stars was considered as very simple without mass loss, metallicity, binarity, mixing and magnetic field effects. The exact importance of these various effects was always disputed, some effects being considered as negligible by some authors and being overestimated by other ones. We show that each of these effects may considerably influence the course of evolution, the lifetimes, the massive star filiations and the nucleosynthesis. Showing some biases in recent studies, we try to appreciate the relative importance of the various effects, which is likely to depend on metallicity Z.